Synthetic light generation device

Abstract

To provide a synthetic light generation device that, in the synthetic light generation device including an optical detector, enables minimizing a length and height as much as possible in a shape of the device, although a size of a width therein is allowable to some extent.SOLUTION: A synthetic light generation device includes: a plurality of light sources that outputs light different in a wavelength; respective optical waveguides and an optical multiplexer in which the light output from the plurality of light sources propagate; an optical multiplexing circuit that includes the optical waveguide outputting multiplex light obtained by the optical multiplexer; and an optical detector. In the optical multiplexing circuit, the synthetic light generation device has a reflection groove that reflects leakage light not propagating in respective optical waveguides, of the light output from the plurality of light sources, in one side lateral face direction, and has the optical detector detecting the reflected leakage light disposed in the one side lateral face direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a composite light generating device for use in an image display device, the composite light generating device comprising: a plurality of light sources outputting light of different wavelengths; an optical multiplexing circuit including optical waveguides to which the light output from the plurality of light sources is input, an optical multiplexer, and an optical waveguide to output the multiplexed light obtained by the optical multiplexer; and a photodetector. [Background technology]

[0002] In recent years, optical multiplexers using multiple laser beams as light sources have become known in composite light generating devices used in the light source portion of image display devices such as eyeglass-type terminals and portable projectors (see Patent Document 1). The optical multiplexers are manufactured through a process in which low-refractive index and high-refractive index silicon oxide films are laminated on a silicon substrate using known chemical vapor deposition (CVD) or sputtering methods, and then patterned by photolithography using a photomask, and further a low-refractive index silicon oxide film is laminated to form an overclad layer.

[0003] Here, it is known that the laser diode that generates the laser light changes or deteriorates depending on the environment during use, such as temperature, humidity, static electricity, and power supply noise, and to address the problem of deterioration, an optical communication module is known in which a photodetector is provided on the rear side opposite to the light emission side of the laser diode, and the light emitted on the rear side is detected and feedback-controlled to stabilize the output of the laser diode (see Patent Document 2). Also known is a composite light generating device that stabilizes the output of a laser diode by providing a photodetector above or below an optical waveguide in an optical multiplexer or the like to which the light emitted from the laser diode is input, detecting leakage light from the optical waveguide in the upward or downward direction, and feedback-controlling the light (see Patent Documents 3 and 4).

[0004] However, in the case where the image display device is a glasses-type terminal and the composite light generating device is incorporated into temples having an approximately rectangular cross-sectional shape, there are various constraints on the shape of the composite light generating device when manufacturing the composite light generating device including a photodetector.For example, the length of the composite light generating device corresponding to the output direction of the laser diode and the height of the composite light generating device (the vertical length of the composite light generating device) must be made as small as possible, but the width of the composite light generating device (the horizontal length of the composite light generating device) can be tolerated up to a certain size.Under these constraints, it was difficult to address the situation using the technology of providing a photodetector on the back side of the laser diode or above or below the optical waveguide in an optical multiplexer, etc. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-195603 A [Patent Document 2] Japanese Patent Application Publication No. 10-253857 [Patent Document 3] JP 2022-143133 A [Patent Document 4] JP 2002-223027 A Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention has been made in consideration of the above circumstances, and is to provide a synthetic light generating device including a photodetector, the shape of which allows a certain degree of tolerance in width while making the length and height as small as possible. [Means for solving the problem]

[0007] The present invention provides a composite light generating device comprising a plurality of light sources that output light of different wavelengths, an optical multiplexing circuit including respective optical waveguides through which the light output from the plurality of light sources propagates, an optical multiplexer, and an optical waveguide that outputs the multiplexed light obtained by the optical multiplexer, and a photodetector, wherein the optical multiplexing circuit has a reflective groove that reflects leakage light that does not propagate through each of the optical waveguides among the light output from the plurality of light sources toward one side, and the photodetector that detects the reflected leakage light is disposed toward the one side.

[0008] It is preferable that the angles of incidence between the central axes of the light beams output from the plurality of light sources and the reflecting grooves are each 48 degrees or more.

[0009] It is preferable that the photodetector is disposed with its light receiving surface facing upward.

[0010] The photodetector preferably includes a plurality of light receiving regions.

[0011] It is preferable that a photodetector is provided for each of the reflected leak lights.

[0012] It is preferable that the plurality of light sources include laser diodes of at least three colors: red, green and blue.

[0013] The present invention also provides an image display device including the above-described composite light generating device. Effect of the Invention

[0014] According to the present invention, a composite light generating device is provided with a plurality of light sources, an optical multiplexing circuit including respective optical waveguides to which the light output from the plurality of light sources is input, an optical multiplexer, and an optical waveguide to which the multiplexed light obtained by the optical multiplexer is output, and a photodetector, in which the optical multiplexing circuit has a reflective groove for reflecting leakage light from the light output from the plurality of light sources that does not propagate through the respective optical waveguides toward one side, and a photodetector for detecting the reflected leakage light is disposed toward the one side, so that the shape of the composite light generating device can be made as small as possible in length and height while allowing a certain degree of width. In addition, since the leakage light is reflected toward one side by the reflective groove, the leakage light output from the output end face of the optical multiplexing circuit as excess light that adversely affects image display can be reduced or eliminated. Here, the leaked light that does not propagate through the optical waveguide refers to both light that is output from the light source but cannot enter the optical waveguide and leaks out, and light that is once input to the optical waveguide but leaks out from the optical waveguide during propagation. [Brief description of the drawings]

[0015] [Figure 1] 1 is a top view of a composite light generating device according to a first embodiment of the present invention. [Diagram 2] FIG. 5 is a top view of a composite light generating device according to a second embodiment of the present invention. [Diagram 3] FIG. 11 is a top view of a composite light generating device according to a third embodiment of the present invention. [Figure 4] 4 is a diagram showing the angle between the central axis of light output from a light source and a reflecting groove. FIG. [Diagram 5] 1 is a side view of a composite light generating device according to a first embodiment of the present invention. [Figure 6] FIG. 2 is a top view of a composite light generating device according to Comparative Example 1, which is a conventional technique. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, examples for carrying out the present invention will be described with reference to the drawings, however, the present invention is not limited to these examples.

[0017] FIG. 1 shows a top view of a composite light generating device 200 according to a first embodiment of the present invention. In the composite light generating device 200, blue light, green light, and red light output from a blue laser diode 1, a green laser diode 2, and a red laser diode 3, which are light sources arranged on the left side, are input to the optical waveguides 4 to 6 from the left end face of the optical multiplexing circuit 100, respectively, propagate, and are multiplexed by the optical multiplexer 7. The multiplexed multiplexed light 9 propagates through the optical waveguide 8 and is output from the right end face. Here, the optical multiplexer 7 conceptually shows a part having a function of multiplexing three types of light input by the optical waveguides 4 to 6 into one multiplexed light by a known means or method using a directional coupler or the like, and then outputting the multiplexed light to the optical waveguide 8, and there is no boundary line that specifically defines the optical multiplexer 7. In addition, the shape of the optical waveguides 4 to 6 was adopted from the shape of the optical waveguide in the composite light generating device described in Patent Application No. 2022-165691 previously filed by the present applicant. The application describes a combined light generating device that can be miniaturized, and the contents of the application can be used not only for the shape of the optical waveguides but also for other shapes, such as the distances between the optical waveguides 4 to 6 at the left end face of the optical multiplexing circuit 100, as long as they do not interfere with the solution of the problems of the present invention.

[0018] The leakage light of the three lights with different wavelengths output from the blue laser diode 1, the green laser diode 2, and the red laser diode 3 that could not enter the optical waveguides 4 to 6 is reflected toward the lower side surface by the reflecting grooves 11 and 12, and the reflected leakage light is detected by the photodetector 10 arranged on the lower side surface. The reflecting groove 11 reflects the leakage light that could not enter the optical waveguides 4 and 5, and the reflecting groove 12 reflects the leakage light that could not enter the optical waveguide 6. Here, the angle of incidence θ between the central axis of the light output from the light source and the reflecting surfaces of the reflecting grooves 11 and 12 is both 45 degrees. The definition of the angle of incidence θ will be described later. According to the law of light reflection, the angle of incidence and the angle of reflection are equal, so the central axis of the reflected leakage light is perpendicular to the central axis of the light output from the light source, and the leakage light is reflected directly downward. Since the photodetector 10 is disposed on the lower side of the optical multiplexing circuit 100, it is difficult to make the width of the composite light generating device 200 as small as possible, and therefore the size of the width must be allowed to a certain extent.

[0019] FIG. 2 shows a top view of a mixed light generating device 201 according to a second embodiment of the present invention. The configuration of the mixed light generating device 201 is the same as that of the mixed light generating device 200 shown in FIG. 1, except that the shape and angle of the reflecting grooves are different. The reflecting grooves 13, 14, and 15 reflect the leaked light that could not be input to the optical waveguides 4, 5, and 6, respectively. The angles of incidence between the central axis of the light output from the light source and the reflecting surfaces of the reflecting grooves 13, 14, and 15 are 55 degrees, 45 degrees, and 35 degrees, respectively, and the angles of incidence and reflection are equal. Therefore, the reflecting groove 13 reflects the leaked light slightly to the right of directly below, the reflecting groove 14 reflects the leaked light directly below, and the reflecting groove 15 reflects the leaked light slightly to the left of directly below. By using the reflecting grooves corresponding to the leaked light that could not be input to the optical waveguide, the degree of freedom of the angle θ with respect to the photodetector 10 is increased. Furthermore, compared to Example 1, by optimally setting an arbitrary incident angle for each reflection groove, it is possible to reflect the leakage light from each of the blue laser diode 1, green laser diode 2, and red laser diode 3 to a narrow area in the lower side surface direction of the optical multiplexing circuit 101. Therefore, the size of the photodetector 10 can be reduced, and the manufacturing cost of the photodetector 10 can be reduced. Even if the size of the photodetector 10 cannot be reduced, the precision error of the position where the photodetector 10 is disposed can be increased, so that manufacturing defects when disposing the photodetector 10 can be reduced, and manufacturing costs can be reduced.

[0020] FIG. 3 shows a top view of a mixed light generating device 202 according to a third embodiment of the present invention. The configuration of the mixed light generating device 202 is the same as that of the mixed light generating device 200 shown in FIG. 1, except that the shape of the reflecting groove is different and the shape of the photodetector is different. The reflecting grooves 16, 17, and 18 reflect the leaked light that could not be input to the optical waveguides 4, 5, and 6, respectively. Since the angles of incidence θ between the central axis of the light output from the light source and the reflecting surfaces of the reflecting grooves 16, 17, and 18 are all 45 degrees, the leaked light is reflected directly downward, as in the mixed light generating device 200. The leaked light reflected by the reflecting grooves 16, 17, and 18 is detected by the photodetectors 19, 20, and 21, respectively. By providing a photodetector corresponding to each of the reflected leaked lights, the laser diodes can be precisely controlled, improving the output stability of the laser diodes.

[0021] FIG. 4 is a diagram showing the central axis of the light output from the light source and the incident angle θ of the reflecting surface of the reflecting groove. Here, as an example, the central axis light 22 (not shown in FIG. 1) output from the blue laser diode 1 in FIG. 1 and the incident angle θ of the reflecting surface of the reflecting groove 11 are shown. The definition of the incident angle θ is the angle between the light 22 output from the light source and the normal to the reflecting surface of the reflecting groove 11. Regarding the reflected light 23 of the light 22 output from the light source, since the reflection angle is equal to the incident angle according to the law of light reflection, it is reflected at a reflection angle θ that is symmetrical to the incident angle with respect to the normal. In addition, for the light 22 output from the light source, the transmitted light 24 that could not be reflected by the reflecting surface is shown, but in the case of total reflection under the conditions described below, the transmitted light 24 is not generated and only the reflected light 23 is generated.

[0022] Here, assuming that the refractive index of silicon dioxide, which is a general cladding material, is 1.46 and the refractive index of the air medium of the reflecting groove is 1.0, it is calculated by Snell's law that the condition for the light 22 output from the light source to be totally reflected by the reflecting surface of the reflecting groove 11 is an incident angle θ of 43 degrees or more. Therefore, in order to generate only the reflected light 23 toward the photodetector 10 without generating the transmitted light 24 in the light 22 output from the light source, it is preferable that the incident angle θ is 43 degrees or more. In addition, since the light output from a laser diode generally has a radiation angle spread of about ±5 degrees, it is more preferable that the incident angle θ is 48 degrees or more if the spread of the radiation angle is taken into consideration.

[0023] FIG. 5 shows a side view of the composite light generating device 200 of the first embodiment shown in FIG. 1, seen from the photodetector 10 side. The light sources arranged on the left side are a red laser diode 3 in the front, a green laser diode 2 and a blue laser diode 1 arranged from the front to the back, and the leaked light that could not be input to the optical waveguides 4 to 6 is reflected toward the front as reflected light 28 to 30 by reflection grooves 11 and 12 (not shown). The optical multiplexing circuit 100 has a cladding layer 26 laminated on a silicon substrate 27 (the optical waveguides 4 to 6, which are the core layers, are not shown), and the photodetector 10 is disposed with the light receiving surface 25 facing upward. The light detector 10 may be disposed vertically so that the light receiving surface 25 faces the reflected light 28 to 30 directly, instead of being disposed with the light receiving surface 25 facing upward. Although the vertical arrangement has the advantage of being able to receive a larger amount of reflected light, the height of the photodetector 10 may be greater than the height of the light sources 1 to 3 and the optical multiplexing circuit 100, so it is preferable to arrange the light receiving surface 25 facing upward in order to reduce the height of the entire composite light generating device 200. When the light receiving surface 25 faces upward, the amount of received light decreases compared to when the light receiving surface 25 is arranged vertically facing the reflected light 28 to 30, but it is possible to receive the reflected light 28 to 30. The photodetector may be a known photodiode or the like, and the output of each laser diode, which is the light source, is stabilized by feedback control according to the change in the detected leak light. The feedback control is not particularly limited, and known controls described in Patent Documents 2 to 4 and the like may be used.

[0024] FIG. 6 shows a top view of a composite light generating device 203 according to Patent Document 2 as Comparative Example 1. The configuration of the composite light generating device 203 is the same as that of the composite light generating device 200 in FIG. 1 except that the photodetector 31 is disposed on the rear side opposite to the side of the emitted light of the laser diode and the optical multiplexer 103 does not have a reflection groove. Since the photodetector is not disposed in the side direction of the optical multiplexer 103, the composite light generating device 203 can be made smaller in width but is obviously longer than the composite light generating device 200 in FIG. 1. In addition, the leakage light that could not be input to the optical waveguides 4 to 6 is output from the right end face of the optical multiplexing circuit 103 as surplus light that adversely affects image display. In contrast, the present invention also has the effect of reducing or eliminating the surplus light output from the right end face of the optical multiplexing circuit 103 by reflecting the leakage light in one side direction by the reflection groove.

[0025] The optical multiplexing circuits 100 to 102 described in the first to third embodiments can be manufactured by using known means and methods described in Patent Document 1 and the like, and the reflecting groove can be processed by known methods such as etching. Although only a parallelogram shape is described for the reflecting groove in the first to third embodiments, the shape is not limited to this and known shapes such as a triangle can also be used. It is preferable that a metal thin film is formed on the bottom surface of the reflecting groove, since this can improve the reflection performance. Furthermore, the optical waveguide may be either a single mode optical waveguide or a multimode optical waveguide.

[0026] Concerning the three lights with different wavelengths output from the blue laser diode 1, the green laser diode 2, and the red laser diode 3 described in the first to third embodiments, since the cone cells in the human retina react to red light, green light, and blue light, it is preferable to include at least blue light, green light, and red light sources, but it may include only two types of light sources as necessary. Laser diodes that output other yellow light, orange light, and purple light may also be used. For each wavelength range, for example, blue light is 430 to 495 nm, green light is 495 to 570 nm, red light is 610 to 770 nm, yellow light is 570 to 595 nm, orange light is 595 to 610 nm, and purple light is 400 to 430 nm. In addition, other light sources such as reflective light-emitting diodes may be used instead of laser diodes. [Industrial Applicability]

[0027] The synthetic light generating device of the present invention can be used as a light source for small image projection devices such as eyeglass-type terminals and portable projectors, and its shape allows for a certain degree of tolerance in width, while making it possible to make the length and height as small as possible. [Explanation of symbols]

[0028] 1. Blue laser diode 2 Green laser diode 3. Red laser diode 4. Optical waveguide into which the output light of the blue laser diode 1 is input 5. Optical waveguide into which the output light of the green laser diode 2 is input 6. Optical waveguide into which the output light of the red laser diode 3 is input 7 Optical multiplexer 8 Optical waveguide through which multiple light propagates 9 Multiple Light 10 Photodetector in Figs. 1 and 2 11 Reflecting groove for reflecting leakage light from the optical waveguides 4 and 5 in FIG. 1 12 Reflecting groove for reflecting leakage light from the optical waveguide 6 in FIG. 1 13 Reflecting groove for reflecting leaked light from the optical waveguide 4 in FIG. 2 14 Reflecting groove for reflecting leaked light from the optical waveguide 5 in FIG. 2 15 Reflecting groove for reflecting leaked light from the optical waveguide 6 in FIG. 2 16 Reflecting groove for reflecting leaked light from the optical waveguide 4 in FIG. 3 17 Reflecting groove for reflecting leaked light from the optical waveguide 5 in FIG. 3 18 Reflecting groove for reflecting leaked light from the optical waveguide 6 in FIG. 3 19 Photodetector of leakage light reflected by the reflecting groove 16 in FIG. 3 20 Photodetector of leaked light reflected by the reflecting groove 17 in FIG. 3 21 Photodetector of leaked light reflected by the reflecting groove 18 in FIG. 3 22 Central axis of the light emitted from the blue laser diode 1 in FIG. 4 23 Reflected light of the light output from the blue laser diode 1 reflected by the reflecting surface in FIG. 4 24 Transmitted light of the light output from the blue laser diode 1 that passes through the reflecting surface in FIG. 4 25 Photosensitive surface 26 Cladding Layer 27 Silicon Substrate 28 Reflection of leaked light that could not be input to the optical waveguide 4 29 Reflected light of leaked light that could not be input to the optical waveguide 5 30 Reflected light of leaked light that could not be input to the optical waveguide 6 31 Photodetector in Figure 6 100 Optical multiplexing circuit in the combined light generating device of the first embodiment 101 Optical multiplexing circuit in the combined light generating device of the second embodiment 102 Optical multiplexing circuit in the combined light generating device of the third embodiment 200 Synthetic light generating device of Example 1 201 Synthetic light generating device of Example 2 202 Synthetic light generating device of Example 3 203 Comparative Example 1 Synthetic Light Generating Apparatus

Claims

1. A composite light generating device comprising: a plurality of light sources that output light of different wavelengths; an optical multiplexing circuit including respective optical waveguides through which the light output from the plurality of light sources propagates, an optical multiplexer, and an optical waveguide that outputs multiplexed light obtained by the optical multiplexer; and a photodetector, wherein the optical multiplexing circuit has a reflective groove that reflects leakage light that does not propagate through each of the optical waveguides among the light output from the plurality of light sources toward one side surface, and the photodetector that detects the reflected leakage light is disposed toward the one side surface.

2. 2. The device for generating composite light according to claim 1, wherein the angles of incidence between the central axes of the light beams output from the plurality of light sources and the reflecting surfaces of the reflecting grooves are each 48 degrees or more.

3. 3. The apparatus for generating composite light according to claim 1, wherein the photodetector is disposed with its light receiving surface facing upward.

4. 3. The apparatus for generating composite light according to claim 1, wherein the photodetector includes a plurality of light receiving regions.

5. 3. The composite light generating device according to claim 1, wherein the photodetector is provided for each of the reflected leaked lights.

6. 3. The apparatus for generating composite light according to claim 1, wherein the plurality of light sources include laser diodes of at least three colors: red, green and blue.

7. An image display device comprising the composite light generating device according to claim 6.

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